semaphore:RedGuest,BlkGuest,ShipGuest,Check,ship,s;
int Red=0,Blk=0;     
RedGuest=0;            /*用于红客登船安全同步*/
BlkGuest=0;            /*用于黑客登船安全同步*/
ShipGuest=4;           /*用于红、黑客等船同步，即船运客未回*/
check=0;               /*用于登船安全检查同步*/
ship=0;                /*开船同步信号*/
s=1;                   /*用于红、黑客登船互斥*/
void RedGuestGetShip(){/*红客登船进程*/
L1:V(check);        /*Call the SafeCheck()*/
    P(ShipGuest);
    P(s);
    P(RedGuest);
    Red=Red+1;
    the RedGuest get ship;
    V(check);           /*Call the SafeCheck()*/
    V(s);
    goto L1;
}

void BlkGuestGetShip(){/*黑客登船进程*/
L2:V(check);        /*Call the SafeCheck()*/
    P(ShipGuest);
    P(s)
    P(BlkGuest);
    Blk=Blk+1;
    the RedGuest get ship;
    V(check);           /*Call the SafeCheck()*/
    V(s);
    goto L2;
}
void SafeCheck(){      /*登船安全检查进程*/
   p(check);
   if(Red+Blk==4)
    {
        V(ship); /*start the ship*/
    }
   if(Red+Blk==3)
     {
        if(Red%2!=0)     /*if Red%2!=0,so there are 3 or 1 RedGuest on ship,*/
           V(RedGuest);  /* then let 1 RedGuest get ship is safe.*/
        else             /*if Red%2==0,so there are 2 or 0 RedGuest on ship,*/
           V(BlkGuest);  /* then let 1 RedGuest get ship is safe.*/
      }
    else
     {
        V(RedGuest);
        V(BlkGuest);
      }
}
void ShipGuest(){        /*船送乘客过河进程*/
   P(ship);
   Ship the Guest to another bank and return;
   Red=0;
   Blk=0;
   V(ShipGuest);
   V(ShipGuest);
   V(ShipGuest);
   V(ShipGuest);
}

</body></html>